In wireless communication systems, particularly in outdoor scenarios (e.g. cellular communication systems, vehicle-to-wayside data communication, etc.) each radio base station may be equipped with several antennas which might be spatially separated by some distance from the base station hardware. Here, the term base station used throughout this invention generally refers to the transmitting/receiving entities of the stationary radio network infrastructure. That is, the term base station also covers Access Points of WLAN based systems, Radio Gateways of Wireless Sensor Networks, etc.
The antennas will typically be mounted in places that cannot easily be accessed, e.g. on roof tops of buildings, on high masts, etc. Even access to the base station hardware (e.g. for maintenance purposes) may be restricted. For example, in Communication Based Train Control (CBTC) systems, particularly in Mass Transit scenarios, base stations are typically installed close to the track and not accessible during hours of train operation. The possibility of performing certain maintenance tasks remotely or at least reducing the time needed for on-site maintenance activities is therefore quite important for ensuring a reliable operation with acceptable costs and effort.
At each base station location, one or more antennas may be connected. The purpose of connecting more than one antenna to a base station can be redundancy, antenna diversity, combination of multiple antennas to achieve some desired coverage pattern, etc. In the conventional art, connections between a base station 101 and N antennas 1031 to 103N are as shown in FIG. 1. The base station 101 has N ports, i.e., Port 1 to Port N. The antennas 1301 to 103N are connected to corresponding ports of the base station 101, respectively, via RF connections 1021 to 102N. The RF connection can be an RF cable such as a coaxial cable. Furthermore, several base stations serving different communication systems may be co-located, with the corresponding antennas mounted on the same mast or at least close to each other. For example, in a current CBTC project for Guangzhou Line 4 Metro, the train control system alone uses up to 8 antennas per base station. Therefore, identification of antennas may sometimes be complicated.
Regarding the aspect of diagnosis of the RF path, current systems employ a concept of mutual monitoring of multiple radio interfaces. In the system currently installed in Guangzhou Line 4 Metro and Beijing Line 10 Metro, each base station has two independent radio interfaces, and RF propagation conditions between these radio interfaces, i.e. involving radio cards, cabling, antennas and radio channel between the corresponding antennas, are measured and evaluated in order to derive hints about defective or degraded components in the signal path. The scheme has some weaknesses due to the inherent transmission over-the-air and is also limited with respect to the identification of the faulty components, i.e. the localization of problems.
Therefore, in such systems the following practical challenges with respect to routine maintenance tasks arise and have been experienced in actual projects:
1. For reference purposes and post-installation troubleshooting and maintenance, it is desirable to maintain comprehensive documentation of the hardware components (e.g. antennas) used and of their characteristics and performance figures as measured before/during the installation. In principle this documentation could be based on a unique serial number printed on each component or attached to it in an electronically readable form, such as barcode or RFID tag. Since antennas cannot easily be accessed after installation, however, it will be hard to read the attached labels printed on the antennas or attached in an electronically readable form when for example it is required to verify correct assignment of antennas to base stations.
2. In order to guarantee the desired coverage, in multi-antenna systems it is essential that each antenna is connected to the correct RF port of the base station. Since in most cases it is impossible to optically trace back the antenna cable (i.e. RF cable) all the way back to the antenna, there is a large potential for mistakes in the assignment of antenna cables to RF ports of the base station. Careful labelling of the antenna cables at both ends can reduce the probability of mistakes, but labels may easily be torn off accidentally, fade over time, may be hard to read without detaching the cable, etc. Additional error sources come into play during maintenance tasks where for example cable pigtails (including labels) are exchanged.
3. Basic but reliable diagnosis functions for ensuring that the RF connection between base station and antenna is intact would be desirable, e.g. basic checking of the integrity of the cable connection and/or of the attenuation between base station and antenna.
A recent trend in cellular communication systems (e.g. 2G and 3G mobile phone networks) is the separation of the RF processing units from the base stations and their integration into so-called Remote Radio Heads which can be located close to the antenna and relatively far away from the bulky protocol and baseband processing units. The Remote Radio Heads are connected to the base stations typically through optical fibre. The approach is costly, requires highly specialized base station hardware and does not by itself solve the problems stated above. For most applications, the cost and complexity to extend the approach to address the above mentioned issues are prohibitively high.
In view of the above, a better way of supporting communication for maintenance and diagnosis purposes is needed between a base station and antennas, such as providing to the base station information relating to the antennas connected with the base station and/or information relating to RF connections connecting with the antennas.